Rotor member for rotary magnetic position indicator

ABSTRACT

A rotor member for a rotary magnetic position indicator incorporating two abutting permanent magnets. The first permanent magnet is cylindrical and has oppositely polarized areas at the respective extremities of a diameter. The second permanent magnet has at least two polar projections joined by cylindrical surface portions, the projections being oppositely polarized. The magnets are oriented with the polarized areas and projections of the same polarity being generally axially aligned.

United States Patent [191 Steele 1 Apr. 2, 1974 1 ROTOR MEMBER FORROTARY MAGNETIC POSITION INDICATOR [75] Inventor: Gilbert V. Steele,Fort Wayne, Ind.

. [73] Assignee: Bowmar Instrument Corporation,

Fort Wayne, Ind.

[22] Filed: Dec. 1, 1972 [21] Appl. No.1 311,435

[52] U.S. Cl 310/156, 310/49, 340/379 [51] Int. Cl. H02k 37/00 [58]Field of Search 310/40, 46, 49, 156, 126;

[56] References Cited UNITED STATES PATENTS 3,631,475 12/1971 Quandt etal. 310/156 X 3,223,865 12/1965 Gladstone t. 3 10/156 X 3,456,138 7/1969Huber 3,588,888 6/1971 Harden 340/378 Primary Examir1erD. F. Duggan [57]ABSTRACT A rotor member for a rotary magnetic position indicatorincorporating two abutting permanent magnets. The first permanent magnetis cylindrical and has oppositely polarized areas at the respectiveextremities of a diameter. The second permanent magnet has at least twopolar projections joined by cylindrical surface portions, theprojections being oppositely polarized. The magnets are oriented withthe polarized areas and projections of the same polarity being generallyaxially aligned.

1 Claim, 9 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates generally to rotary magnetic positionindicators, and more particularly to a rotor member for such indicators.

2. Description of the Prior Art Rotary magnetic position indicators arecommonly employed for displaying discrete indicia in response to thecharacters of a prearranged code. A common type of such indicatorcomprises a permanent magnet rotor member and a stator structure havingselectively energizable field windings thereon, the rotor carrying adrum having the indicia displayed on its surface. Selective energizationof the field windings causes the magnetic axis of the rotor to alignitself with respective poles of the field structure thereby to providethe desired rotational indication.

' One common form of rotary magnetic position indicator, such as thatshown in U.S. Pat. No. 3,371,333 assigned to the Assignee of the presentapplication, employsa cylindrical permanent magnet .rotormember, whileanother common form, as shown in US. Pat. Nos. 3,416,015 and 3,478,349,both assigned to the Assignee of the present application, employs apermanent magnet rotor member having salient poles.

' A cylindrical permanent magnet rotor member provides maximum fluxdensity acting on the currentcarrying conductors of the stator thusproviding maximum rotating or starting torque'however, by virtue of theuniform air gap provided by the cylindrical configuration, a minimumclogging or locking effect is provided, i.e., a tendency to maintain arotor locked-in at a given position in the power-off condition. On theother hand, while a much greater clogging or locking I effect isprovided by a permanent magnet rotor member having salient poles,substantially greater stator emf is required in order to rotate therotor member away from a given position, and an increase in the startingtorque by increasing the air gap is accompanied by a decrease in thelocking torque. Furthermore, due to the limitations involves difficultcalculations and expensive I trial and error, and inherently involvescompromise. It

is therefore desirable to provide a permanent magnet rotor member 'for arotary magnetic position indicator which will satisfy both requirementsindependently with minimum interaction thereby to provide optimumoperation of the indicator.

SUMMARY OF THE INVENTION In its broader aspects, the invention providesa rotor member for a rotary magnetic position indicator, the rotormember having an axis and comprising a permanent magnet structure whichincludes a first permanent section having a cylindrical outer surfacecoaxial with the axis, and a second permanent magnet section axiallycontiguous with the first section and having at least two polarprojections joined by cylindrical surface portions coaxial with theaxis, the first section having oppositely polarized areas at its outersurface, and the second section projections being oppositely polarized,the areas and projections of the same polarity being generally axiallyaligned.

' It is accordingly an object of the invention to provide an improvedrotor member for a rotary magnetic position indicator.

Another object of the invention is to provide an improved permanentmagnet rotor member for a rotary magnetic position indicator whichprovides both adequate starting torque and locking torque.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side cross-sectional viewillustrating one embodiment of a rotary magnetic position indicatorincorporating the invention;

FIG. 2 is a top view, partly in cross section, taken along the line 22of FIG. 1, showing the improved rotor member of the invention andschematically showing the stator structure;

FIG. 3 is a schematic illustration showing the electrical connection ofthe coils of the indicator of FIGS. 1

and 2;

FIG. 4 is a top view of the cylindrical permanen magnet employed in theimproved rotor member of the invention;

FIG. 5 is a top view showing the cylindrical andsalient pole permanentmagnets in assembled relation;

FIG. 6 is a cross-section view taken generally along the line 6-6 ofFIG. 5;

FIG. 7 is a fragmentary cross-sectional view taken along the same lineas FIG. 6 but showing another embodiment of the invention;

FIG. 8 is a fragmentary cross-sectional view showing yet anotherembodiment of the invention; and

FIG. 9 is a top view showing adaptation of the improved rotor member ofthe invention for use in a different form of stator structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 through6 of the drawings, the invention is described and illustrated inconnection with a rotary magnetic position indicator, generally indicated at 10, having an odd number of positions, as further describedand illustrated in US. Pat. No. 3,735,303 granted May 22, 1973, and alsoassigned to the assignee of the present application.

Indicator 10 comprises a base board 14 formed of suitable insulatingmaterial and which may have the conductors which are connected to thecoils of the indicator printed thereon. A cup-shaped member 16 formed ofsuitable non-magnetic metal is provided having its bottom 18 adhered tobase board 14. Side wall 20 of cup-shaped member 16 has shoulder 22formed therein which supports stator core member 24. Stator 3 coremember 24 may be adhesively secured in its assembled position.

Shaft 26 has projection aligned openings 30, 32 in bottom 18 ofcup-shaped member 16 and base board 14, being secured therein bysuitable adhesive material 34. Flange 36 on shaft 26 abuts the innersurface of bottom 18 of cup-shaped member 16 and'is adhesively securedthereto.

Stator core member 24 is formed of suitable magnetic material and hasyoke portion 38 with an odd number, shown here as eleven,'radiallyinwardly extending, equally angularly spaced polar projections or teeth40 formed thereon. Teeth 40 have inner ends 42 mutually defining a borefor receiving permanent magnet rotor member 44.

.A distributed winding is provided on stator core member 24 comprisingeleven coils 46 respectively spanning three adjacent teeth 40. Referringadditionally to FIG. 3, ends 48 of coils 46 are connected to- ;gether bya common connection 50 which may be a printed circuit connection on baseboard 14, common connection 50 being connected to one side of source 52of direct current. The other ends 54 are connected, as by printedcircuit connections on base board 14, to the switching system shownschematically at 56, which selectively couples coils 46, one at a time,for energization across source52 so that the inner end 42 of arespective stator tooth 40 is polarized with a given polarity, such asNorth.

The stator core and winding arrangement thus far described is that shownin the aforesaid application Ser. No. 190,150 and does not form a partof the present invention.

Rotor assembly 44 comprises two abutting permanent magnets 58, 60adhesively secured to sleeve member 62. 'Sleeve member 62 is rotatablymounted on shaft 26'by suitable bearings 64, 66 separated by spacer 68surrounding shaft 26. Drum 70 formed of suitable material, such asaluminum, has inner flange 72 adhesively secured to hub portion 74 ofsleeve member 62, and outer flange-76 upon which the indicia aredisplayed.

Upper extension portion 78 of shaft 26 is located and supported by frameelements 80, 82, mounted on base board 14. Lower bearing 64 engagesthrust washer 84 seated on shoulder 86 on shaft 26, and the rotorassembly 44 is held in assembled relation by snap ring 88 which engagesupper bearing 66.

Referring now additionally to FIGS. 4 through 6, permanent magnet 60 hascylindrical outer surface 90 and is polarized along magnetic axis 92coincident with a diameter of magnet 60 to form oppositely polarizedareas 94, 96 at the extremities of the diameter.

In accordance with the teachings of the aforesaid U.S. Pat. No.3,735,303 permanent magnet 58 has a first polar projection 98 and twopolar projections 100-1, 100-2. Each of the polar projections 98, 100has an-outer end having generally the same angular extent as the innerends 42 of stator teeth 40. Projections 100-1, 100-2 are equally spacedon opposite sides of diameter 102, and are respectively aligned with anadjacent pair of stator teeth 40. Projection 98 is aligned with anotherstator tooth 40, as shown in FIG. 2. Projections 98, 100 are joined bycylindrical surface portions 104. Permanent magnet 58 is magnetized on amagnetic axis coincident with diameter 102 thereby to polarizeprojections 98 with one polarity such as South,

28 which extends through I .4' and projections 100-1, 100-2 with theopposite polarity, such as North.

In this embodiment, cylindricalpermanent magnet 60 and salient polepermanent magnet 58'are oriented so that their respective magnetic axes92, 102 are in axial alignment with South polar projection 98 and Northpolar projections 100-1, 100-2 respectively axially aligned with Southpolararea 94 and North polar area 96 of cylindrical permanent magnet 60.i

It will be observed that cylindrical surface 90 of cylindrical magnet 60and cylindrical surface portions 104 of permanent magnet 58 are coaxialwith axis 106 of shaft 26.

In the specific embodiment illustrated, as best seen in FIG. 5, thediameter of permanent magnet 58 taken across polar projections 98, 100is slightly less than the diameter of cylindrical permanent magnet 60.However, the diameters may be the same, or the diameter of permanentmagnet 58 may be slightly greater than the diameter of cylindricalmagnet 60, the relative diameters of permanent magnet 58 vis-a-vispermanent magnet 60 being a variable which is selectively adjustable inorder to provide optimum starting andlock-in torques.

It will also be observed by reference to FIGS. 1 and 6 that salient polepermanent magnet 58 is axially thicker than cylindrical permanent magnet60, the relative thicknesses of the two permanent magnets being anothervariable which may be selectively adjusted in order to provide optimumstartingand lock-in torques.

In the embodiment of FIGS. 1-6, permanent magnets 58, 60 are twoseparate magnets in abutting relation.

Referring now to FIG. 7 in which some elements are indicated by primedreference numeralsan integral pertion 60', as shown the configuration ofthe integral permanent magnet 108 otherwise being identical to that ofthe abutting permanent magnets 58, 60 of the previous I figures.

Referring now to FIG 8 in which similar elements are indicated by doubleprimed reference numerals, whether integrally formed as described abovein conriection with FIG. 7, or formed as two separate magnets asdescribed above in connection with FIGS. 1 6, the diameter of permanentmagnet 60 or permanent magnet section 60 may be the same, orapproximately the same as the diameter of the cylindrical surfaceportions 104, 104" of the permanent magnet 58 or permanent magnetsection 58", with projections 98", 100 (not shown in FIG 8) projectingradially outwardly beyond cylindrical surface of permanent magnets 60 orpermanent magnet section 60".

Referring now to FIG. 9 in which like elements are indicated by likereference numerals and similar elements by triple primed referencenumerals, the salient pole permanent magnet 58" is shown as having twodiametrically opposite polar projections 98", thus rendering thepermanent magnet rotor suitable for use in a stator structure of thetype shown for example in the aforesaid U.S. Pat. No. 3,478,349. Here,the magnetic and grain axes of the two magnets 58", may be axiallyaligned, as shown by dashed lines 110. Alternatively, as furtherdescribed in the aforesaid U.S. Pat. Nos. 3,416,015 and 3,478,349, themagnetic and grain axes of the salient pole permanent magnet 58 may bealigned with one corner of polar projections 98", 100", as shown by thedashed line 112, and the magnetic and grain axes of magnet 60 beingaligned with the centers of the polar projections, as shown by dashedline 110. A further alternative is to align the magnetic and grain axesof permanent magnet 58" with the center of the projections, as shown bydashed line 110, and to align the magnetic and grain axes of permanentmagnet 60 with the corners of the projections, as shown by dashed line114. Still further, where two separate magnets are employed wth one ofthe permanent magnets being substantially thicker than the other, thegrain axis of the salient pole permanent magnet 58" may be aligned withone corner of each polar projection 98", 100" as shown by dashed line112, the grain axis of cylindrical permanent magnet 60 may be alignedwith the opposite corners of projections 98", 100" as shown by dashedline 114, and two permanent magnets may be magnetized simultaneouslyalong the center line of the projections, as shown by dashed line 110resulting in a magnetic unbalance which provides the desired detentaction.

While there have been described above the principles of this inventionin connection with specific apparatus,

it is to be'clearly understood that this description is made only by wayof example and not as a limitation to the scope of the invention.

What is.claimed is:

1. A rotor member for a rotary magnetic position indicator, said rotormember having an axis and comprising a permanent magnet structure whichincludes a first permanent magnet section having a cylindrical outersurface coaxial with said axis, and a second permanent magnet sectionaxially contiguous with said first section and having at least two polarprojections joined by cylindrical surface portions coaxial with saidaxis, saidfirst section having oppositely polarized areas at said outersurface thereof, said second section projections being oppositelypolarized, said areas and projections of the same polarity beinggenerally aaxially aligned, there being three of said polar projections,one of said projections having one polarity and having one extremity ofsaid second section magnetic axis extending substan tially through thecenter thereof, the other two of said projections having the oppositepolarity and being spaced on opposite sides of the other extremity ofsaid second section magnetic axis.

1. A rotor member for a rotary magnetic position indicator, said rotormember having an axis and comprising a permanent magnet structure whichincludes a first permanent magnet section having a cylindrical outersurface coaxial with said axis, and a second permanent magnet sectionaxially contiguous with said first section and having at least two polarprojections joined by cylindrical suface portions coaxial with saidaxis, said first section having oppositely polarIzed areas at said outersurface thereof, said second section projections being oppositelypolarized, said areas and projections of the same polarity beinggenerally aaxially aligned, there being three of said polar projections,one of said projections having one polarity and having one extremity ofsaid second section magnetic axis extending substantially through thecenter thereof, the other two of said projections having the oppositepolarity and being spaced on opposite sides of the other extremity ofsaid second section magnetic axis.